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Subject[ 59/72] [SCSI] scsi_scan: Fix Poison overwritten warning caused by using freed shost
3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Huajun Li <huajun.li.lee@gmail.com>

commit 267a6ad4aefaafbde607804c60945bcf97f91c1b upstream.

In do_scan_async(), calling scsi_autopm_put_host(shost) may reference
freed shost, and cause Posison overwitten warning.
Yes, this case can happen, for example, an USB is disconnected just
when do_scan_async() thread starts to run, then scsi_host_put() called
in scsi_finish_async_scan() will lead to shost be freed(because the
refcount of shost->shost_gendev decreases to 1 after USB disconnects),
at this point, if references shost again, system will show following
warning msg.

To make scsi_autopm_put_host(shost) always reference a valid shost,
put it just before scsi_host_put() in function
scsi_finish_async_scan().

[ 299.281565] =============================================================================
[ 299.281634] BUG kmalloc-4096 (Tainted: G I ): Poison overwritten
[ 299.281682] -----------------------------------------------------------------------------
[ 299.281684]
[ 299.281752] INFO: 0xffff880056c305d0-0xffff880056c305d0. First byte
0x6a instead of 0x6b
[ 299.281816] INFO: Allocated in scsi_host_alloc+0x4a/0x490 age=1688
cpu=1 pid=2004
[ 299.281870] __slab_alloc+0x617/0x6c1
[ 299.281901] __kmalloc+0x28c/0x2e0
[ 299.281931] scsi_host_alloc+0x4a/0x490
[ 299.281966] usb_stor_probe1+0x5b/0xc40 [usb_storage]
[ 299.282010] storage_probe+0xa4/0xe0 [usb_storage]
[ 299.282062] usb_probe_interface+0x172/0x330 [usbcore]
[ 299.282105] driver_probe_device+0x257/0x3b0
[ 299.282138] __driver_attach+0x103/0x110
[ 299.282171] bus_for_each_dev+0x8e/0xe0
[ 299.282201] driver_attach+0x26/0x30
[ 299.282230] bus_add_driver+0x1c4/0x430
[ 299.282260] driver_register+0xb6/0x230
[ 299.282298] usb_register_driver+0xe5/0x270 [usbcore]
[ 299.282337] 0xffffffffa04ab03d
[ 299.282364] do_one_initcall+0x47/0x230
[ 299.282396] sys_init_module+0xa0f/0x1fe0
[ 299.282429] INFO: Freed in scsi_host_dev_release+0x18a/0x1d0 age=85
cpu=0 pid=2008
[ 299.282482] __slab_free+0x3c/0x2a1
[ 299.282510] kfree+0x296/0x310
[ 299.282536] scsi_host_dev_release+0x18a/0x1d0
[ 299.282574] device_release+0x74/0x100
[ 299.282606] kobject_release+0xc7/0x2a0
[ 299.282637] kobject_put+0x54/0xa0
[ 299.282668] put_device+0x27/0x40
[ 299.282694] scsi_host_put+0x1d/0x30
[ 299.282723] do_scan_async+0x1fc/0x2b0
[ 299.282753] kthread+0xdf/0xf0
[ 299.282782] kernel_thread_helper+0x4/0x10
[ 299.282817] INFO: Slab 0xffffea00015b0c00 objects=7 used=7 fp=0x
(null) flags=0x100000000004080
[ 299.282882] INFO: Object 0xffff880056c30000 @offset=0 fp=0x (null)
[ 299.282884]
...

Signed-off-by: Huajun Li <huajun.li.lee@gmail.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/scsi/scsi_scan.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -1815,6 +1815,7 @@ static void scsi_finish_async_scan(struc
}
spin_unlock(&async_scan_lock);

+ scsi_autopm_put_host(shost);
scsi_host_put(shost);
kfree(data);
}
@@ -1841,7 +1842,6 @@ static int do_scan_async(void *_data)

do_scsi_scan_host(shost);
scsi_finish_async_scan(data);
- scsi_autopm_put_host(shost);
return 0;
}

@@ -1869,7 +1869,7 @@ void scsi_scan_host(struct Scsi_Host *sh
p = kthread_run(do_scan_async, data, "scsi_scan_%d", shost->host_no);
if (IS_ERR(p))
do_scan_async(data);
- /* scsi_autopm_put_host(shost) is called in do_scan_async() */
+ /* scsi_autopm_put_host(shost) is called in scsi_finish_async_scan() */
}
EXPORT_SYMBOL(scsi_scan_host);




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